3M Scotch-Weld DP420 Black?

[Jonathan S.]

3M Scotch-Weld DP420 Black, merits thereof for ski binding mounting, specifically for desperately short screw lengths in shockingly light skis, surprisingly recommended by La Sportiva -- discuss.

Background info:

http://solutions.3m.com/wps/portal/3...4871756&rt=rud
http://www.amazon.com/3M-Scotch-Weld...r&pageNumber=1
http://www.golfwrx.com/forums/topic/...oxy-questions/

I'm thinking that same G/Flex that I used for a cracked edge repair (thanks to CSSmith for the rec, but no thanks to that lurking rock on the GoS trail back on April 16) could also be just as good for this context:

http://www.jamestowndistributors.com...do?part=115873

[neufox47]

Is the epoxy only to prevent screws from loosening or is it also to increase the amount of force necessary to pull the screw out of the core?

[Jonathan S.]

Is the epoxy only to prevent screws from loosening or is it also to increase the amount of force necessary to pull the screw out of the core?

Must be the latter since these are the default instructions for regular mounts (as opposed to threaded inserts):

[tuco]

I'm betting a good seal is no small part of the recommendation.

[DoWork]

Scotch weld is some serious shit. We use the #2214 250 degree-cure stuff for industrial micro screen repairs and although it's kind of expensive and you can only buy it in a 6 pack it's crazy effective.

If 3M says it will work, I believe them. They really do make the best stuff.

[DoWork]

Is the epoxy only to prevent screws from loosening or is it also to increase the amount of force necessary to pull the screw out of the core?

Both. Looking at the specs it's got a 50lb/in peel strength and a 4500lb/in^2 shear strength. The shear strength is the key though as that's the forces we are working with for the most part.

Basically it would take a very serious application of force to get those screws out. That's a badass epoxy.

I guess the peel strength would lend itself to helping keep the screws from just ripping out but that's probably more of a function of the core itself than the epoxy. That said if you painted the binding interface that would definitely help keep it on there too.

[Jonathan S.]

Thanks, very interesting, but ... in light of all this, I don't recall any unusual difficulty in removing the screws on DarkStar's Plum 165 heel units (which had been mounted with DP420 by Skimo Co) when we remounted his Nano skis for Plum 185 heel units -- is that surprising?
(Or perhaps am I not remembering any such screw removing difficulty in light of having to grind down new ungunked screws and also helicoiling the two old holes we were able to reuse: what an ordeal!)

[bfree]

The shear strength is irrelevant for this application considering cohesive failure of the epoxy isn't going to be the failure (or extraction) mode. You'll either get substrate failure of the wood core and threads, or more likely get adhesion failure at the interface. Adhesion is mostly a factor of the surface finishes and cleanliness, and it's pretty damn hard to get those holes very clean. DP420 is a good structural epoxy, easy to use, and commonly found.

[DoWork]

Thanks, very interesting, but ... in light of all this, I don't recall any unusual difficulty in removing the screws on DarkStar's Plum 165 heel units (which had been mounted with DP420 by Skimo Co) when we remounted his Nano skis for Plum 185 heel units -- is that surprising?
(Or perhaps am I not remembering any such screw removing difficulty in light of having to grind down new ungunked screws and also helicoiling the two old holes we were able to reuse: what an ordeal!)

Actually yes that is surprising. Perhaps a function of the core more than the epoxy? Hard to say really.

[Jonathan S.]

[...]Basically it would take a very serious application of force to get those screws out. That's a badass epoxy.[...]

[...]I don't recall any unusual difficulty in removing the screws on DarkStar's Plum 165 heel units (which had been mounted with DP420 by Skimo Co) when we remounted his Nano skis for Plum 185 heel units -- is that surprising?
(Or perhaps am I not remembering any such screw removing difficulty in light of having to grind down new ungunked screws and also helicoiling the two old holes we were able to reuse: what an ordeal!)

The shear strength is irrelevant for this application considering cohesive failure of the epoxy isn't going to be the failure (or extraction) mode. You'll either get substrate failure of the wood core and threads, or more likely get adhesion failure at the interface.[...]

Actually yes that is surprising. Perhaps a function of the core more than the epoxy? Hard to say really.

Putting all these different observations together, I think it all makes sense now: the screws were tight, yet not insanely so.

But upon removal, they were all gunked up with the then-mysterious blackness, and the two old holes on each ski that could be reused (i.e., shared with both the original Plum 165 and replacement 185) had to be helicoiled.

The DP420 wasn't going to let go of those screws, but instead the core just kind of crumbled apart as the screw was turned, leaving me with gunked-up screws and blown-out holes.

Perhaps the conclusion is that DP420 is indeed impressively strong epoxy, yet unnecessarily and even pointlessly strong for such an application given the strength of what it's being bonded to?